German laid-open document DE 10 2009 051 819 A1 discloses a pendant switch for a crane, the operating elements of which can be activated and deactivated by means of a safety circuit. The safety circuit comprises an RFID reading device, which is arranged in the pendant switch, and an RFID transponder which is worn in the form of an armband by an operating person authorised to operate the crane. The RFID reading device has a signal strength with a small range of about 20 cm to 30 cm. The safety circuit ensures that the operating elements of the pendant switch are only activated and thus the crane also only remains operable for as long as an authorised operating person is located in sufficient proximity to the control switch, i.e. the RFID transponder is in the receiving range of the RFID reading device. As soon as the operating person or his RFID transponder becomes too far removed from the receiving range of the RFID reading device, the operating elements of the pendant switch are deactivated by means of the safety circuit.
Moreover, the web page (www.hbc-radiomatic.com) of HBC-radiomatic GmbH describes under the product name “radiomatic pilot” a wireless control switch for a crane which comprises a micro joystick and an inclination sensor as operating elements. Arranged on the micro joystick is a so-called dead-man's button which has to be pressed by a thumb in order to be able to operate the micro joystick. This is intended to prevent crane functions from being triggered unintentionally. The inclination sensor in the control switch is activated by a release button, which is pressed by an index finger, on the underside of the control switch. As soon as the release button is released, the inclination sensor is deactivated. Lifting or lowering movements and travel movements of a crane trolley can be initiated by means of the inclination sensor.
Furthermore, German laid-open document DE 199 21 349 A1 discloses a dead-man's control for a circular saw. The circular saw comprises a trimming table which can be moved by means of a feed drive. The feed drive can be controlled by means of a rotary handle. In order to prevent the feed drive from running inadvertently or without supervision, the dead-man's control is provided in the form of a capacitive, inductive, mechanical and/or electrical sensor in the region of the rotary handle. This ensures that when an operating person contacts the rotary handle the presence of the operating person is detected, which triggers a release of the feed drive by means of the dead-man's control.